Ion implantation is an alternative method to diffusion for injecting impurities into a semiconductor layer. Ion implantation is typically a process in which ions that have been accelerated by several kilovolts are made to penetrate a solid surface such as silicon, and, unlike the ions in a typical diffusion process, can be made to do this at room temperature. Ion implantation generally produces the maximum concentration of implanted material beneath the surface of the wafer. Because the implanted dopants are generally not in the proper lattice position and are mostly electrically inactive, a high temperature annealing process is often used which repairs crystal damage and electrically activates the dopants.
Implantation of oxygen into silicon is generally a preferred process for building silicon-on-insulator (SOI) substrates which can be used, for example, in very large scale integration (VLSI) devices. This separation by implantation of oxygen (SIMOX) process generally involves three steps:
A) A standard silicon wafer is cleaned in a clean room ambient to substantially remove any received contaminants.
B) Oxygen is implanted under the surface of the wafer at relatively high energy (e.g. 2.times.10.sup.18 /cm.sup.2 of oxygen atoms at 200 keV).
C) The wafer is annealed at high temperature (e.g. greater than about 1300.degree. C. for 6 hours) to substantially repair implant damage and form the buried oxide layer.
SIMOX wafers are of interest because they can generally be used to provide one or more of the following advantages over bulk silicon wafers:
A) better radiation hardness
B) higher speed performance
C) higher temperature operation
D) lower power devices
E) lower cost process for some applications
F) easier implementation of submicrometer design rules.
Recent improvements in the quality of SIMOX wafers, along with the advent of readily available processing equipment, have helped to stimulate an increased interest in SIMOX technology. "The Status of SIMOX Technology" by Michael A. Guerra, Solid State Technology, November 1990, pp. 75-78, discusses SIMOX technology and advances in the field.